This invention relates to pneumatic actuators for use with musical instruments. More particularly, this invention relates to such pneumatic actuators as used in player pianos or similar instruments.
The use of pneumatic actuators for various musical instruments is well known. Traditionally, a player piano uses a plurality of pneumatic actuators corresponding on a one-to-one basis with the piano keys. Each actuator is connected to a vacuum source and includes a bellows which closes when a signal tube senses a hole in a paper tape, the paper tape being programmed with the particular musical selection.
Although pneumatic actuators have been in use for a long period of time, there have been significant problems with the actuators. Complexity of construction and relatively high cost of manufacture have been among the most common problems. Other significant problems have been failure of the bellows cloth or material due to pinch-induced wear upon it. Requirements for numerous small parts have complicated the assembly of most prior art musical instrument pneumatic actuators.
With reference now to FIG. 1, a particular prior art pneumatic actuator 10 will be discussed in detail. In particular, the pneumatic actuator 10 is shown operatively connected to a piano key 12 of a player piano by way of a push rod 14 the actuator 10 is mounted upon a support rod 16 and secured by set screw 18. The support rod or bar 16 extends between two wooden blocks such as the single block 20 shown in FIG. 1. The pneumatic actuator 10 includes upper and lower aluminum body pieces 22 and 24 respectively. The upper and lower body pieces are pivotably connected together by a bellows cloth or material 26 which is glued in a sealing fashion along the side edges of parts 22 and 24 and the front edges (adjacent push rod 14) of those pieces. The bellows 26 is of course flexible material such that it will fold when the pieces 22 and 24 are brought together in the manner described below.
The upper body piece 22 includes a front portion 28 connected to a valve cover portion 30 by way of an offset portion 32. A felt or similar fabric cloth 34 covers an atmospheric port 36, which port is a hole in the valve cover portion 30 bounded by a circular upper valve seat 38 made of plastic. The upper body piece 22 further includes a vacuum chamber enclosing portion 40 having a vacuum port 42 surrounded by a lower valve seat 44 having an annular portion extending around the outside of port 42 and a rim portion disposed above the port 42 as shown. Seated upon the lower valve seat 44 is a valve member having a disk-like valving portion 46V attached to a stem portion 46S. The stem portion 46S is operable for up and down movement under the influence of a pouch 48 mounted on a platform 70. The pouch in turn is operable in known fashion based upon the pressure signal on signal tube 50, which signal tube is mounted upon a plastic piece 52 slid into an opening extending completely across the upper back portion of the vacuum chamber enclosing portion 40 and adhered thereto. The piece 52 further includes a vacuum tube 54 which is hollow and communicates with a round vacuum hole (not shown) to the interior of the vacuum chamber defined by vacuum chamber enclosing portion 40 and sealed on its sides by bellows 26 and its upper back portion by the plastic piece 52 itself.
The operation of the actuator 10 of FIG. 1 will now be described. In the position shown in FIG. 1, the signal tube 50 is closed off from the atmosphere as a tube (not shown) extends to a tracker bar (not shown) covered by the paper tape of a player piano. That is, the paper tape indicates that the note corresponding to that particular actuator should not be depressed. The vacuum chamber defined within the vacuum chamber enclosing portion 40 will be evacuated due to the connection of a vacuum pump to the vacuum tube 54. The valve portion 46V will be disposed upon the lower valve seat 44 such that the lower bellows chamber 56 and upper bellows chamber 58 will be at atmospheric pressure due to air passing through the filter or felt piece 34 and the atmospheric port 36. The push rod 14 will be disposed in the position shown with a rubber piece 60 trapped within a groove on the upper front side of the lower body piece 24 simply resting against the push rod 14. When the signal tube 50 is opened to the atmosphere by way of the player piano paper tape having a slot indicating that the note corresponding to this actuator should be played, air flows into the signal tube 50 pushing up on the pouch 48 which in turn displaces upwardly the valve stem 46S and the integral valve portion 46V such that the valve portion 46V now is resting up against the upper valve seat 38. The vacuum pump (not shown) connected to the vacuum chamber by way of vacuum tube 54 is now in communication with the lower and upper bellows chambers 56 and 58 by way of the vacuum port 42. As the air is drawn out of the lower and upper bellows chambers 56 and 58, the bellows cloth 56 folds together and brings the lower body piece 24 up essentially adjacent to the upper body piece 22 along the length thereof. This upward movement of the lower body piece 24 (clockwise movement relative to a pivot point at the far right end of lower body piece 24) will cause the rubber piece 60 mounted within the aluminum lower body piece 24 to push up on the rod 14. This in turn lifts the back of the piano key 12 bringing the front of the key downward by virtue of the fulcrum (not shown).
Although the prior art actuator of FIG. 1 has been generally useful, the bellows material 26 has had a tendency to wear quickly. Specifically, breaks in the bellows material often occur. Additionally, the assembly of the separate plastic valve seats 36 and 44 within the aluminum upper body piece 22 as well as the assembly of the separate plastic piece 52 within the upper body piece 22 has been time consuming and difficult to accomplish. Further, after repeated use of the device there has been a tendency of the upper body piece 22 to warp or distort which may place added strain upon the bellows piece 26. The assembly of the valve member having portions 46V and 46S requires the drilling of a hole in the valve cover portion 30, which hole is larger than the diameter of the disk-like portion 46V. A corresponding hole also must be drilled in the vacuum chamber enclosing portion 40, the latter hole being just below the first mentioned hole. The lower valve seat 44 must then be placed within the hole after it has been sufficiently deburred. The valve would then be inserted. In order to capture the valve and provide a proper valve seat, the ring-like upper valve seat 38 must then be placed in the hole which was drilled in the valve cover portion 30. The signal tube 50 extends through a hole in the plastic piece 52 and into a platform which communicates with a zone underneath the pouch 42, and proper alignment of these holes is quite difficult. Finally, the use of glue to attach the bellows piece 26 to the upper and lower body pieces 22 and 24 often causes problems due to run off of excess glue.